Guest Post: introducing Kukufeldia

Today Paul Barrett generously gives up his time to write about the newly named igunaodonitan dinosaur Kukufeldia and the problems of providing definitions and diagnoses of new taxa in the fossil record:

What are the criteria that palaeontologists use when proposing a new species? Historically, many different categories of information have been used to justify naming new taxa, most often the recognition of unique morphology. However, new names have also been erected on the basis of material that is not anatomically distinctive, but which hails from previously unexplored or undocumented geographical regions or time periods. Currently, the ‘ideal’ basis for identifying a new taxon would be to find material that possesses clear unambiguous features that are unique to that species (known technically as ‘autapomorphies’), although where such features are not present specimens with unique combinations of characters also have currency. However, it needs to be remembered that even autapomorphies can be shown to have wider distributions within groups of organisms as more species are described, so that features once considered unique and diagnostic can become commonplace. A good example of this phenomenon, which has been termed ‘obsolescence’, comes from the sauropod dinosaur genus ‘Titanosaurus’ (Wilson & Upchurch 2003). When named in 1877, on the basis of isolated vertebrae from the latest Cretaceous of India, ‘Titanosaurus’ could be distinguished on the basis of its strongly procoelous caudal vertebrae (in which the articular ball of the vertebra is on the rear surface), a feature that was absent in all other sauropods named at that time. However, numerous discoveries have since demonstrated that procoely is widespread among sauropods (in titanosaurs in general and some ‘mamenchisaurs’, for example) and as a result, could not be regarded as a reliable diagnostic feature for ‘Titanosaurus’.

As the type material of this genus can no longer be shown to possess either autapomorphies or a unique character combination, it has since been sunk into the taxonomic limbo of nomen dubium (i.e. an invalid species). These kinds of historical problems have led to an aspiration (or desire) to name new species on better specimens that have the potential to offer as much anatomical information as possible. Nevertheless, it should be remembered that it is not the quantity of material that is important per se (for example, many beautiful, complete hadrosaur skulls were given their own names in the past and are now considered as junior synonyms of other taxa), but its quality. In this sense quality does not refer to the completeness or preservational state of the specimen, but its informativeness. A poorly preserved single element can still fulfil all of the criteria to serve as a robust, name-bearing type specimen if it can be demonstrated to be unique beyond reasonable doubt, whereas an almost complete specimen would be useless if missing those features that might allow it to be recognised as either something new or as a referred specimen of an existing species.

All of these points have a strong bearing on a series of current controversies surrounding a plexus of iguanodontian dinosaur species from the Lower Cretaceous Wealden Group of southern England and its equivalents in western Europe. Historically, all of the large ornithopod dinosaurs from these deposits have been attributed to the genus Iguanodon, although a large number of species were recognised (I. anglicus, I. atherfieldensis, I. bernissartensis, I. dawsoni, I. fittoni, I. hollingtonensis, I. mantelli, I. seeleyi and several other iguanodontian genera such as Sphenospondylus and Vectisaurus). Detailed work by David Norman recognised that several of these species were probably the same taxon (e.g. I. fittoni and I. hollingtonensis). However, more recently many of these species have been shown to be distinct from Iguanodon and removed to genera of their own (Paul 2007, 2008; Norman 2010). These include the new genera Barilium (Norman 2010: for ‘I.’ dawsoni), Dollodon (Paul 2008: for a specimen previously referred to ‘I.’ atherfieldensis), Hypselospinus (Norman 2010: for ‘I.’ fittoni and ‘I.’ hollingtonensis) and Mantellisaurus (Paul 2007: for ‘I.’ atherfieldensis). As several authors were working independently, but simultaneously, on these specimens, a recent paper by Carpenter & Ishida (2010) added to this list with several other new names: Proplanicoxa, Sellacoxa, Torilion and Wadhurstia. Wadhurstia refers to the specimen formerly called ‘I.’ fittoni and Torilion to ‘I.’ dawsoni – however, as Norman (2010) had already provided replacement names for these species, the new names proposed by Carpenter & Ishida (2010) instantly become junior objective synonyms of Norman’s new names (Hypselospinus and Barilium, respectively). Sellacoxa was erected for a specimen that Norman (2010) regards as an individual of Barilium and Proplanicoxa for a specimen previously regarded as ‘I.’ atherfieldensis (or Vectisaurus). As a result of this work, the taxonomy of these animals has become considerably more complex, with little agreement among authors on the criteria used to pull specimens apart into different species. Nevertheless, it does seem that the diversity of these faunas was higher than has generally been appreciated.

The right jaw of the holotype of Kukufeldia. From McDonald et al., 2010

Adding to these discussions was a paper by Andrew McDonald, myself and Sandra Chapman, naming a new species of iguanodontian on the basis of a single right dentary from the classic Wealden locality of Cuckfield (McDonald et al. 2010). This dentary, housed in the collections of the Natural History Museum, was acquired by Captain Lambart Brickenden and presented to Gideon Mantell, who subsequently described it as a jaw of Iguanodon in 1848. Since that time it has gone largely unnoticed in the museum’s collection and was only mentioned in passing in a handful of nineteenth century publications, that is until Andrew spent time examining the iguanodontians in our basement as part of his PhD research. Andrew initially noted some unusual features of the jaw and our further discussions convinced us that it possessed a combination of features that allowed it to be distinguished from all other iguanodontians. In particular, the dentary possesses one clear autapomorphy: a secondary row of small holes for blood vessels and nerves that extends behind and sub-parallel to the usual, and more conspicuous, row of such holes that is commonly present in other ornithischian dinosaurs. As we compared the ‘Brickenden jaw’ with other iguanodontians, our conviction that this specimen represented something different from existing Wealden taxa grew. Eventually this led to us to submit a paper on the specimen to the journal Zootaxa, where we described it as Kukufeldia tilgatensis, honouring the Cuckfield locality. Although the material described is fragmentary, and not the ideal specimen that one might wish for as a holotype, it is taxonomically informative and currently bears a feature that is otherwise unknown elsewhere among iguanodontians. It may be that Kukufeldia ultimately proves to be referable to one of the other named Wealden iguanodontians, but until overlapping material of sufficient quality is present to test that possibility, the unique nature of its anatomy suggests that it is useful to regard it as a new species, representing a morphology that was previously unrecognised.

Given this recent flurry of activity, a period of consolidation is now required to assess the validity of all of these taxa and to find consensus upon which specimens can be confidently referred to each species. The differing opinions of these authors, as well as the features that their analyses share in common (there are some!), illustrate well the need to assess objectively the information offered by a specimen when deciding on whether it is sufficiently distinctive to deserve its type status.

Paul, G. S. 2007. Turning the old into the new: a separate genus for the gracile iguanodont from the Wealden of England. 69–77. In Carpenter, K. (ed.) Horns and beaks: ceratopsian and ornithopod dinosaurs. Indiana University Press, Bloomington and Indianapolis, 369 pp.

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8 Responses to “Guest Post: introducing Kukufeldia”

Just wanted to throw in a note about Wilson and Upchurch’s (2003) “obsolescent” terminology, which I hope not to see perpetuated.

For those not already familiar with this, W&U wrote (p152), under the heading `Obsolescent’ features:

“At the time of his writing, the species-defining characters listed by Lydekker (1877) were unique to `Titanosaurus indicus‘ among dinosaurs (e.g. presence of procoelous distal caudal vertebrae). These features now obtain a broad distribution among titanosaurs. Thus, species-defining characters (autapomorphies) have obsolesced into characters defining larger groups (synapomorphies) over time, through the discovery of new and better skeletons.”

What they are describing here are not obsolescent features, but obsolete features. (Obsolescent means in the process of becoming obsolete, but a feature like the procoelous caudals of “Titanosaurus” is obsolete right now.) So I think we’d better serve clarity if we called change the terminology before it starts to get entrenched.

I know this seems like a small point, but we may as well get it right as wrong.

As I buzzed through your post, I halted at your discussion of obsolescent (or “obsolete” as you call them) characters. They don’t come up very often in discussions for whatever reason but they are certainly relevant when we are talking about early holotypes – so it is great you dragged it out of obscurity. In the spirit of venturing into something even more arcane, I thought I would chime in to clarify our (Paul U. and my) intent in using the word “obsolescent” in lieu of the much more obvious word “obsolete” in the character context. You are correct that “obsolescent” refers to something that is in the process becoming obsolete, whereas “obsolete” refers to the finished product. Paul and I wanted to describe a process by which characters drift from their original, envisioned home towards ever more remote places on the tree. In other words, character distributions change over time because new fossils are found and new interpretations are made that change them, if ever so slightly. We wanted to avoid the word “obsolete” because to us it gave the sense that the process stops and characters stay fixed. I realize that you and others may be looking at this from the perspective of a particular clade of interest, e.g., character 1 is now “obsolete” for X clade and so on. Although this is slightly different than what we had in mind, I don’t have a problem with that usage – it is technically correct – but if you use it in this sense it requires a “clade X” and becomes more or less synonymous with the word “symplesiomorphic”.

OK, that makes sense — I see why Jeff and Paul went with the term “obsolescent”. That said, I still think it’s misleading: the characters are, flatly, obsolete for the purpose for which they were originally proposed. I suppose you could call them something like repurposed characters or relocated characters, but I think that would be worse.

It’s nice to see Kukufeldia getting a bit of press! Thanks to Paul for blogging about it and to Dave for hosting the post. I’m revising a paper at the moment that deals with many of the recent machinations in British iguanodont taxonomy, so I shouldn’t say too much right now. I will say that I agree with Norman that the holotype of Sellacoxa is referable to Barilium.

Thanks for the nice words Andy. I’m well aware that I don’t cover enough of the ornithischians here, but I do know how confused the taxonomy is. Good luck with that, and do let us know when the paper is out!